Abstract
Fatty acids (FAs) have been implicated in signaling roles in plant defense responses. We previously reported that mutation or RNAi-knockdown (OsSSI2-kd) of the rice OsSSI2 gene, encoding a stearoyl acyl carrier protein FA desaturase (SACPD), remarkably enhanced resistance to blast fungus Magnaporthe oryzae and the leaf-blight bacterium Xanthomonas oryzae pv. oryzae (Xoo). Transcriptomic analysis identified six AAA-ATPase family genes (hereafter OsAAA-ATPase1–6) upregulated in the OsSSI2-kd plants, in addition to other well-known defense-related genes. Here, we report the functional analysis of OsAAA-ATPase1 in rice’s defense response to M. oryzae. Recombinant OsAAA-ATPase1 synthesized in Escherichia coli showed ATPase activity. OsAAA-ATPase1 transcription was induced by exogenous treatment with a functional analogue of salicylic acid (SA), benzothiadiazole (BTH), but not by other plant hormones tested. The transcription of OsAAA-ATPase1 was also highly induced in response to M. oryzae infection in an SA-dependent manner, as gene induction was significantly attenuated in a transgenic rice line expressing a bacterial gene (nahG) encoding salicylate hydroxylase. Overexpression of OsAAA-ATPase1 significantly enhanced pathogenesis-related gene expression and the resistance to M. oryzae; conversely, RNAi-mediated suppression of this gene compromised this resistance. These results suggest that OsAAA-APTase1 plays an important role in SA-mediated defense responses against blast fungus M. oryzae.
Highlights
Salicylic acid (SA) plays an important signaling role in plant defense activation against pathogens
We conducted a functional analysis of OsAAA-ATPase1, one of the six AAA-ATPase genes upregulated in OsSSI2-kd rice plants [12]
We previously identified a group of six AAA-ATPase genes (OsAAA-ATPase1–6) that were upregulated in OsSSI2-kd rice plants [12]
Summary
Salicylic acid (SA) plays an important signaling role in plant defense activation against pathogens. Map-based cloning of one of the ssi mutants (ssi2) revealed that the corresponding gene (SSI2) encodes a stearoyl-ACP desaturase, which desaturates stearoyl (18:0)-ACP into oleoyl-ACP, and into oleic acid (18:1) [7]. Disruption of this gene in ssi results in a ten-fold increase in 18:0 fatty acid (FA) content, indicating involvement of FAs in plant defense reactions [7]. The ssi mutant plants accumulate high levels of SA and display constitutive PR gene expression and enhanced resistance to Peronospora parasitica, Pseudomonas syringae [8], and Cucumber mosaic virus [7,9,10]
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